TRAPPIST-1b

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TRAPPIST-1b
TRAPPIST-1 b comparison.png
Earth and TRAPPIST-1b compared
Discovery [1]
Discovered by Michaël Gillon et al.
Discovery site TRAPPIST
Discovery dateMay 2, 2016
Transit
Orbital characteristics [2]
0.01154 ± 0.00010 AU (1,726,000 ± 15,000 km)
Eccentricity 0.00622±0.00304 [3]
1.510826 ± 0.000006 d (36.25982 ± 0.00014 h)
Inclination 89.728°±0.165°
336.86°±34.24° [3]
Star TRAPPIST-1 [4]
Physical characteristics [2]
1.116+0.014
−0.012
  R🜨
Mass 1.374±0.069  M🜨
Mean density
5.425+0.265
−0.272
  g/cm3
1.102±0.052 g
10.80±0.51  m/s2
Temperature 397.6±3.8  K (124.5 °C; 256.0 °F, equilibrium) [5]
503+26
−27
  K
(230 °C; 446 °F, surface) [6]
Atmosphere
Composition by volume None or extremely thin [6] [7]

    TRAPPIST-1b is a mainly rocky exoplanet orbiting around the ultra-cool dwarf star TRAPPIST-1, located 40.7 light-years (12.5 parsecs ) away from Earth in the constellation of Aquarius. The planet was detected using the transit method, where a planet dims the host star's light as it passes in front of it. It was first announced on May 2, 2016, [1] and later studies were able to refine its physical parameters.

    Contents

    The planet is about 37% more massive than Earth and about 39% larger in volume; thus its density is very similar. It is the innermost of seven planets orbiting TRAPPIST-1, all of which are terrestrial, but is too close to its star to be in the habitable zone. Observations by the James Webb Space Telescope announced in 2023 suggest that it does not have any significant atmosphere. [6] [7] Its albedo is very low, making it dark in color.

    Physical characteristics

    Mass, radius, and temperature

    TRAPPIST-1b is very similar in both mass, radius, and gravity to Earth. It has a radius of 1.116  R🜨 , a mass of 1.374  M🜨 , and about 110% Earth's surface gravity. [2] Initial estimates of the planet's density suggested that it is not entirely rocky; with a density of 3.98 g/cm3, about ≤5% of its mass must be volatiles, likely in the form of a thick Venus-like atmosphere due to it receiving nearly four times more energy than Earth does. [3] However, refined density estimates show that the planet is only slightly less dense than Earth. [2]

    Assuming the presence of an atmosphere, the planet's surface temperature was initially estimated to be between 750 K (477 °C; 890 °F) and 1,500 K (1,230 °C; 2,240 °F), potentially as high as 2,000 K (1,730 °C; 3,140 °F). This is much hotter than the surface of Venus and may be hot enough that the surface is molten lava. [3] An observation of the secondary eclipse of TRAPPIST-1b by the James Webb Space Telescope, announced in 2023, suggests that the planet does not have any significant atmosphere, with a measured surface temperature of about 503 K (230 °C; 446 °F), [6] [7] and a low albedo. [8] The planet may be very geologically active due to tidal squeezing similar to Jupiter's moon Io, which happens to have a similar orbital period and eccentricity (see TRAPPIST-1#Resonance and tides for references).

    Orbit

    TRAPPIST-1b orbits very close to its parent star. One orbit requires only 36 hours, or about 1.51 Earth days. [9] It orbits about 0.0115  AU (1.72 million  km ; 1.07 million  mi ) from its star, just 1.2% the distance between Earth and the Sun. [3] The close proximity to its host star means that TRAPPIST-1b is likely tidally locked. It also has a very circular orbit, with an eccentricity of 0.00622, significantly more circular than Earth's orbit, which has an eccentricity of 0.0167086.

    Host star

    TRAPPIST-1b orbits the ultracool red dwarf star TRAPPIST-1. It has a mass of 0.089 M and is only 0.121 R, with a surface temperature of 2,511 K (2,238 °C; 4,060 °F) and an age between 3 and 8 billion years. The Sun, in comparison, has a surface temperature of 5,778 K (5,505 °C; 9,941 °F) and is about 4.5 billion years old. TRAPPIST-1 is also very dim, with a luminosity about 0.0005 times that of the Sun. It is too faint to be seen with the naked eye, having an apparent magnitude of 18.80.

    Atmosphere

    Artist's impression of TRAPPIST-1b (March 2023) Rocky exoplanet TRAPPIST-1 b (illustration) (weic2309a).jpg
    Artist's impression of TRAPPIST-1b (March 2023)

    The combined transmission spectra of TRAPPIST-1 b and c rule out cloud-free hydrogen-dominated atmospheres for both planets, so they are unlikely to harbor extended gas envelopes. Also, no helium emission from TRAPPIST-1b has been detected. [10] Prior to JWST observations, other atmospheres, from a cloud-free water-vapor atmosphere to a Venus-like atmosphere, remained consistent with the featureless spectra. [11]

    In 2018, the planet's atmosphere was better examined by the Spitzer Space Telescope and suggested to be quite large and hot, although the presence of an atmosphere could not be confirmed. The planet's transmission spectrum and refined density estimate suggested two main possibilities for the atmosphere: one rich in carbon dioxide, or one rich in water vapor. The more likely CO2 atmosphere would have a scale height of approximately 52 kilometers (32 miles) (Earth's being 8 km (5.0 mi), and Venus' at 15.9 km (9.9 mi)) and an average temperature in excess of 1,400 K (1,130 °C; 2,060 °F), far greater than the planet's equilibrium temperature of 397.6 K (124.5 °C; 256.0 °F). A water vapor atmosphere would need to have a scale height of >100 km (62 mi) and a temperature >1,800 K (1,530 °C; 2,780 °F) to produce the variations seen in the planet's transit depths and its transmission spectrum, and would be vulnerable to photodissociation where CO2 would not be. Other sources for the effects seen, such as hazes and thick clouds, would require an even larger atmosphere. TRAPPIST-1b will have to be studied further to confirm its potential large atmosphere. [9] [3]

    An observation of the secondary eclipse of TRAPPIST-1b by the James Webb Space Telescope, announced in March 2023, suggests that the planet does not have any significant atmosphere. [6] [7] Atmospheres containing carbon dioxide with surface pressures greater than 0.1  bar can be ruled out at 3-sigma, and pressures greater than 0.01 bar at 1-sigma. [8] Further studies of the exoplanet by transmission spectroscopy (primary eclipse), reported in September 2023, also confirmed the absence of a hydrogen-rich atmosphere, but due to stellar contamination were unable to determine the presence or absence of other types of atmospheres based on the transmission spectroscopy data alone. This does not affect the previous results based on emission spectroscopy. [12] [13]

    See also

    Related Research Articles

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    <span class="mw-page-title-main">TRAPPIST-1</span> Ultra-cool red dwarf star in the constellation Aquarius

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    TRAPPIST-1d, is a small exoplanet, which orbits on the inner edge of the habitable zone of the ultracool dwarf star TRAPPIST-1, located 40.7 light-years away from Earth in the constellation of Aquarius. The exoplanet was found by using the transit method. The first signs of the planet were announced in 2016, but it was not until the following years that more information concerning the probable nature of the planet was obtained. TRAPPIST-1d is the second-least massive planet of the system and is likely to have a compact hydrogen-poor atmosphere similar to Venus, Earth, or Mars. It receives just 4.3% more sunlight than Earth, placing it on the inner edge of the habitable zone. It has about <5% of its mass as a volatile layer, which could consist of atmosphere, oceans, and/or ice layers. A 2018 study by the University of Washington concluded that TRAPPIST-1d might be a Venus-like exoplanet with an uninhabitable atmosphere. The planet is an eyeball planet candidate.

    <span class="mw-page-title-main">TRAPPIST-1c</span> Rocky exoplanet orbiting TRAPPIST-1

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    References

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